1. Field of the Invention
The invention relates to hybrid electric vehicle powertrains having an internal combustion engine and an electric drive system with an electric motor, a generator and a battery. It relates also to pure electric vehicle powertrains having an electric motor, a generator and a battery defining an electromechanical power flow path.
2. Background Art
Hybrid electric vehicle powertrains and pure electric vehicle powertrains use a battery and an electric motor to establish a power flow path to vehicle traction wheels. In the case of a hybrid electric vehicle, an internal combustion engine complements the electric motor and the battery by establishing an independent power flow path to the vehicle traction wheels.
One class of hybrid electric vehicles, commonly referred to as a parallel hybrid electric vehicles, includes a powertrain with two power source configurations. The first configuration comprises an engine, a motor, a generator with a battery, and a planetary gearset for coordinating power distribution to traction wheels. A second power source configuration in a parallel hybrid electric powertrain includes an electric drive system with only a motor, a generator and a battery. The battery acts as an energy storing device for the generator and the motor.
The two power source configurations work together seamlessly with the planetary gearset to meet the driver's demand for power as much as possible without exceeding power limits of the powertrain and power limits of the battery subsystem. Under normal operating conditions, a vehicle system controller interprets the driver's demand for power as a function of acceleration or deceleration. The controller will determine how much torque each power source needs to contribute to total power demanded by the driver and to achieve specified vehicle performance (i.e., engine fuel economy, emission quality, driveability, etc.).
The power supplied by the two power sources is coordinated by the vehicle system controller as it meets the driver's demand for power without exceeding the limits of the system and without exceeding the battery voltage limits during either charging or discharging.
The powertrain will determine the driver's demand for torque and achieve optimum division of power between the two power sources without exceeding battery power limits. If the battery limits are exceeded and the battery voltage is outside of a specified precalibrated range, the controller will shut down the vehicle. This condition can be avoided using a closed loop power control as described in co-pending patent application Ser. No. 10/248,886, filed Feb. 27, 2003 entitled “Closed Loop Power Control System for Hybrid Electric Vehicles.” This co-pending application is assigned to the assignee of the present invention. Reference is made to it to complement the present disclosure. It is incorporated in this disclosure by reference.
In a conventional vehicle powertrain with a gasoline engine, combustion energy availability is the same under all operating conditions regardless of the amount of gasoline in the vehicle gas tank. In contrast, the energy availability in a hybrid electric vehicle powertrain or in a pure electric vehicle powertrain depends upon battery conditions (e.g., battery state of charge and battery temperature). A power command to the electric motor in a hybrid electric vehicle or in a pure electric vehicle therefore is limited by the battery power availability.
Accuracy in establishing the battery power limits is needed to maintain the battery voltage within a certain range to ensure that the powertrain system will function properly. Accuracy of the battery limits is needed also to avoid shutdown of the electric motor and its controller due to a voltage that is under or over the battery voltage limits. It is possible, however, for the battery controller to inaccurately estimate the battery's discharge and charge power limits, especially in view of the complexity of electro chemistry of the battery. An inaccurate estimation of the battery power limits could cause the battery voltage to be out of a precalibrated proper range.